Abstract: Over the past few decades, superconducting circuits have been used to realize various novel electronic devices such as quantum bits, SQUIDs, parametric amplifiers, etc. One domain, however, where superconducting circuits fall short is information storage. Superconducting memories are based on the quantization of magnetic flux in superconducting loops. Standard implementations store information as magnetic flux quanta in a superconducting loop interrupted by two Josephson junctions (i.e., a SQUID). However, due to the large inductance required, the size of the SQUID loop cannot be scaled below several micrometers, resulting in low-density memory chips. Here, we propose a scalable memory consisting of a voltage-biased superconducting ring threaded by a half-quantum flux bias. By numerically solving the time-dependent Ginzburg-Landau equations, we show that applying a time-dependent bias voltage in the microwave range constitutes a writing mechanism to change the number of stored flux quanta within the ring. Since the proposed device does not require a large loop inductance, it can be scaled down, enabling a high-density memory technology. (C) 2019 Author(s).

Abstract: Our calculations, within known limitations of Ginzburg-Landau theory, are fully correct and valid for transport phenomena in asymmetric mesoscopic superconductors, deep in the superconducting state. We deemed the experiments of Burlakov et al. [JETP Lett. 86, 517 (2007)] relevant and important to mention in the general context of our paper since the observed shifts in the oscillations of different quantities are qualitatively similar, even though those measurements are performed close to the superconducting-normal state transition in the so-called Little-Parks regime.

Abstract: Oriented attachment of PbSe nanocubes can result in the formation of two-dimensional (2D) superstructures with long-range nanoscale and atomic order. This questions the applicability of classic models in which the superlattice grows by first forming a nucleus, followed by sequential irreversible attachment of nanocrystals, as one misaligned attachment would disrupt the 2D order beyond repair. Here, we demonstrate the formation mechanism of 2D PbSe superstructures with square geometry by using in situ grazing-incidence X-ray scattering (small angle and wide angle), ex situ electron microscopy, and Monte Carlo simulations. We observed nanocrystal adsorption at the liquid/gas interface, followed by the formation of a hexagonal nanocrystal monolayer. The hexagonal geometry transforms gradually through a pseudo-hexagonal phase into a phase with square order, driven by attractive interactions between the {100} planes perpendicular to the liquid substrate, which maximize facet-to-facet overlap. The nanocrystals then attach atomically via a necking process, resulting in 2D square superlattices.

Abstract: Organic photovoltaic (OPV) devices are on the verge of commercialization being long-term stability a key challenge. Morphology evolution during lifetime has been suggested to be one of the main pathways accounting for performance degradation. There is however a lack of certainty on how specifically the morphology evolution relates to individual electrical parameters on operating devices. In this work a case study is created based on a thermodynamically unstable organic active layer which is monitored over a period of one year under non-accelerated degradation conditions. The morphology evolution is revealed by compositional analysis of ultrathin cross-sections using nanoscale imaging in scanning transmission electron microscopy (STEM) coupled with electron energy-loss spectroscopy (EELS). Additionally, devices are electrically monitored in real-time using the non-destructive electrical techniques capacitance-voltage (C-V) and Impedance Spectroscopy (IS). By comparison of imaging and electrical techniques the relationship between nanoscale morphology and individual electrical parameters of device operation can be conclusively discerned. It is ultimately observed how the change in the cathode contact properties occurring after the migration of fullerene molecules explains the improvement in the overall device performance. (C) 2014 Elsevier B.V. All rights reserved.

Abstract: Optical and electronic properties of black phosphorus strongly depend on the number of layers and type of stacking. Using first-principles calculations within the framework of density functional theory, we investigate the electronic properties of bilayer black phosphorus with an interlayer twist angle of 90 degrees. These calculations are complemented with a simple (k) over right arrow . (p) over right arrow model which is able to capture most of the low energy features and is valid for arbitrary twist angles. The electronic spectrum of 90 degrees twisted bilayer black phosphorus is found to be x-y isotropic in contrast to the monolayer. However x-y anisotropy, and a partial return to monolayer-like behavior, particularly in the valence band, can be induced by an external out-of-plane electric field. Moreover, the preferred hole effective mass can be rotated by 90 degrees simply by changing the direction of the applied electric field. In particular, a +0.4 (-0.4) V angstrom(1) out-of-plane electric field results in a similar to 60% increase in the hole effective mass along the y (x) axis and enhances the m(y)*/m(x)* (m(x)*/m(y)*) ratio as much as by a factor of 40. Our DFT and (k) over right arrow . (p) over right arrow simulations clearly indicate that the twist angle in combination with an appropriate gate voltage is a novel way to tune the electronic and optical properties of bilayer phosphorus and it gives us a new degree of freedom to engineer the properties of black phosphorus based devices.

Abstract: On the basis of a simplified Hamiltonian for transition metal impurities in diluted magnetic semiconductors (DMS), the nature of ferromagnetism in p-type III-V DMS are investigated. Ferromagnetism is governed by the Anderson-Hubbard parameter for 3d electrons of Mn2+ and their strong hybridization with the hole carriers in the semiconducting medium. The origin of ferromagnetism in these materials has similarity with the Zener mechanism. From the energetically preferable parallel orientation of Mn spins the Curie temperature is calculated for GaAs:Mn. (C) 2002 Published by Elsevier Science B.V.

Abstract: Objective. The aim was to evaluate the optical properties, mechanical properties and aging stability of yttria-stabilized zirconia with different compositions, highlighting the influence of the alumina addition, Y2O3 content and La2O3 doping on the translucency. Methods. Five different Y-TZP zirconia powders (3 commercially available and 2 experimentally modified) were sintered under the same conditions and characterized by X-ray diffraction with Rietveld analysis and scanning electron microscopy (SEM). Translucency (n = 6/group) was measured with a color meter, allowing to calculate the translucency parameter (TP) and the contrast ratio (CR). Mechanical properties were appraised with four-point bending strength (n = 10), single edge V-notched beam (SEVNB) fracture toughness (n = 8) and Vickers hardness (n = 10). The aging stability was evaluated by measuring the tetragonal to monoclinic transformation (n = 3) after accelerated hydrothermal aging in steam at 134 degrees C, and the transformation curves were fitted by the Mehl-Avrami-Johnson (MAJ) equation. Data were analyzed by one-way ANOVA, followed by Tukey's HSD test (alpha = 0.05). Results. Lowering the alumina content below 0.25 wt.% avoided the formation of alumina particles and therefore increased the translucency of 3Y-TZP ceramics, but the hydrothermal aging stability was reduced. A higher yttria content (5 mol%) introduced about 50% cubic zirconia phase and gave rise to the most translucent and aging-resistant Y-TZP ceramics, but the fracture toughness and strength were considerably sacrificed. 0.2 mol% La2O3 doping of 3Y-TZP tailored the grain boundary chemistry and significantly improved the aging resistance and translucency. Although the translucency improvement by La2O3 doping was less effective than for introducing a substantial amount of cubic zirconia, this strategy was able to maintain the mechanical properties of typical 3Y-TZP ceramics. Significance. Three different approaches were compared to improve the translucency of 3YTZP ceramics. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Abstract: Novel 3DOM BiVO4/TiO2 nanocomposites with intimate contact were for the first time synthesized by a hydrothermal method in order to elucidate their visible-light-driven photocatalytic performances. BiVO4 nanoparticles and 3DOM TiO2 inverse opal were fabricated respectively. These materials were characterized by XRD, XPS, SEM, TEM, N2 adsorption–desorption and UV-vis diffuse (UV-vis) and photoluminescence spectroscopies. As references for comparison, a physical mixture of BiVO4 nanoparticles and 3DOM TiO2 inverse opal powder (0.08 : 1), and a BiVO4/P25 TiO2 (0.08 : 1) nanocomposite made also by the hydrothermal method were prepared. The photocatalytic performance of all the prepared materials was evaluated by the degradation of rhodamine B (RhB) as a model pollutant molecule under visible light irradiation. The highly ordered 3D macroporous inverse opal structure can provide more active surface areas and increased mass transfer because of its highly accessible 3D porosity. The results show that 3DOM BiVO4/TiO2 nanocomposites possess a highly prolonged lifetime and increased separation of visible light generated charges and extraordinarily high photocatalytic activity. Owing to the intimate contact between BiVO4 and large surface area 3DOM TiO2, the photogenerated high energy charges can be easily transferred from BiVO4 to the 3DOM TiO2 support. BiVO4 nanoparticles in the 3DOM TiO2 inverse opal structure act thus as a sensitizer to absorb visible light and to transfer efficiently high energy electrons to TiO2 to ensure long lifetime of the photogenerated charges and keep them well separated, owing to the direct band gap of BiVO4 of 2.4 eV, favourably positioned band edges, very low recombination rate of electron–hole pairs and stability when coupled with photocatalysts, explaining the extraordinarily high photocatalytic performance of 3DOM BiVO4/TiO2 nanocomposites. It is found that larger the amount of BiVO4 in the nanocomposite, longer the duration of photogenerated charge separation and higher the photocatalytic activity. This work can shed light on the development of novel visible light responsive nanomaterials for efficient solar energy utilisation by the intimate combination of an inorganic light sensitizing nanoparticle with an inverse opal structure with high diffusion efficiency and high accessible surface area.

Abstract: Nonthermal atmospheric pressure plasmas are gaining increasing attention for biomedical applications. However, very little fundamental information on the interaction mechanisms between the plasma species and biological cells is currently available. We investigate the interaction of important plasma species, such as OH, H2O2, O, O3, as well as O2 and H2O, with bacterial peptidoglycan by means of reactive molecular dynamics simulations, aiming for a better understanding of plasma disinfection. Our results show that OH, O, O3, and H2O2 can break structurally important bonds of peptidoglycan (i.e., CO, CN, or CC bonds), which consequently leads to the destruction of the bacterial cell wall. The mechanisms behind these breakups are, however, dependent on the impinging plasma species, and this also determines the effectiveness of the cell wall destruction.

Abstract: Nonequilibrium plasmas offer a pathway for energy-efficient CO2 conversion through vibrationally induced dissociation. However, the efficiency of this pathway is limited by a rise in gas temperature, which increases vibrational−translational (VT) relaxation and quenches the vibrational levels. Therefore, we investigate here the effect of plasma pulsing on the VT nonequilibrium and on the CO2 conversion by means of a zerodimensional chemical kinetics model, with self-consistent gas temperature calculation. Specifically, we show that higher energy efficiencies can be reached by correctly tuning the plasma pulse and interpulse times. The ideal plasma pulse time corresponds to the time needed to reach the highest vibrational temperature. In addition, the highest energy efficiencies are obtained with long interpulse times, that is, ≥0.1 s, in which the gas temperature can entirely drop to room temperature. Furthermore, additional cooling of the reactor walls can give higher energy efficiencies at shorter interpulse times of 1 ms. Finally, our model shows that plasma pulsing can significantly improve the energy efficiency at low reduced electric fields (50 and 100 Td, typical for microwave and gliding arc plasmas) and intermediate ionization degrees (5 × 10−7 and 10−6).

Abstract: NiTi is one of the most popular shape-memory alloys, a phenomenon resulting from a martensitic transformation. Commercial NiTi-based alloys are often thermally treated to contain Ni4Ti3 precipitates. The presence of these precipitates can introduce an extra transformation step related to the so-called R-phase. It is believed that the strain field surrounding the precipitates, caused by the matrixprecipitate lattice mismatch, lies at the origin of this intermediate transformation step. Atomic-resolution transmission electron microscopy in combination with geometrical phase analysis is used to measure the elastic strain field surrounding these precipitates. By combining measurements from two different crystallographic directions, the three-dimensional strain matrix is determined from two-dimensional measurements. Comparison of the measured strain matrix to the eigenstrain of the R-phase shows that both are very similar and that the introduction of the R-phase might indeed compensate the elastic strain introduced by the precipitate.

Abstract: New polymorphs of NaMnO2 have been observed using transmission electron microscopy and synchrotron X-ray powder diffraction. Coherent twin planes confined to the (NaMnO2) layers, parallel to the (10 (1) over bar) crystallographic planes of the monoclinic layered rock-salt-type alpha-NaMnO2 (O3) structure, form quasi-periodic modulated sequences, with the known alpha-and beta-NaMnO2 polymorphs as the two limiting cases. The energy difference between the polymorphic forms, estimated using a DFT-based structure relaxation, is on the scale of the typical thermal energies that results in a high degree of stacking disorder in these compounds. The results unveil the remarkable effect of the twin planes on both the magnetic and electrochemical properties. The polymorphism drives the magnetic ground state from a quasi-1D spin system for the geometrically frustrated alpha-polymorph through a two-leg spin ladder for the intermediate stacking sequence toward a quasi-2D magnet for the beta-polymorph. A substantial increase of the equilibrium potential for Na deintercalation upon increasing the concentration of the twin planes is calculated, providing a possibility to tune the electrochemical potential of the layered rock-salt ABO(2) cathodes by engineering the materials with a controlled concentration of twins.

Abstract: New hybrid materials-photosensitized nanocomposites containing nanocrystal heterostructures with spatial charge separation, show high response for practically important sub-ppm level NO2 detection at room temperature. Nanocomposites ZnO/CdSe, ZnO/(CdS@CdSe), and ZnO/(ZnSe@CdS) were obtained by the immobilization of nanocrystals-colloidal quantum dots (QDs), on the matrix of nanocrystalline ZnO. The formation of crystalline core-shell structure of QDs was confirmed by HAADF-STEM coupled with EELS mapping. Optical properties of photosensitizers have been investigated by optical absorption and luminescence spectroscopy combined with spectral dependences of photoconductivity, which proved different charge localization regimes. Photoelectrical and gas sensor properties of nanocomposites have been studied at room temperature under green light (max = 535 nm) illumination in the presence of 0.12-2 ppm NO2 in air. It has been demonstrated that sensitization with type II heterostructure ZnSe@CdS with staggered gap provides the rapid growth of effective photoresponse with the increase in the NO2 concentration in air and the highest sensor sensitivity toward NO2. We believe that the use of core-shell QDs with spatial charge separation opens new possibilities in the development of light-activated gas sensors working without thermal heating.

Abstract: Nb-rich precipitates in the matrix of as-cast and annealed Ni45.5Ti45.5Nb9 alloys are investigated by scanning and scanning transmission electron microscopy, including slice-and-view and geometric phase analysis (GPA). The Nb-rich bcc nano-precipitates in the as-cast alloy have a 10% lattice parameter difference with the B2 matrix and reveal compensating interface dislocations. The 3D reconstruction of the configuration of small Nb-rich precipitates in the annealed alloy reveals a wall-like distribution of precipitates, which may increase the thermal hysteresis of the material.

Abstract: Nanostructured core−shell microspheres with a rough rutile core and a thin anatase shell are synthesized via a one-step heterogeneous templated hydrolysis process of TiCl4 vapor on the aerosol water−air interface. The rutile-in-anatase core−shell structure has been evidenced by different electron microscopy techniques, including electron energy-loss spectroscopy and 3D electron tomography. A new mechanism for the formation of a crystalline rutile core inside the anatase shell is proposed based on a statistical evaluation of a large number of electron microscopy data. We found that the control over the TiCl4 vapor pressure, the ratio between TiCl4 and H2O aerosol, and the reaction conditions plays a crucial role in the formation of the core−shell morphology and increases the yield of nanostructured microspheres.